1. Field of the Invention
The present invention relates to a semiaromatic polyamide resin composition which causes a metal mold to be less fouled at the time of producing molded articles, exhibits excellent anti-creeping property under high-temperature and high-humidity conditions, and makes it possible to efficiently produce molded articles.
2. Description of the Prior Art
A variety of semiaromatic polyamides having impact resistance have heretofore been proposed. For example, Japanese Laid-Open Patent Publication No. 108855/1992 is disclosing a process for producing a polyamide composition comprising a modified elastic copolymer and a semiaromatic polyamide which is composed of an alkylenediamine unit (b) and a dicarboxylic acid unit (a) that comprises 50 to 100 mol % of a terephthalic acid unit and 0 to 40 mol % of an aromatic dicarboxylic acid other than terephthalic acid or a straight-chain aliphatic dicarboxylic acid unit having 6 to 18 carbon atoms.
It has been known that a composition comprising such a semiaromatic polyamide and a modified elastic polymer exhibits excellent heat resistance and impact resistance (Japanese Laid-Open Patent Publications Nos. 41318/1990 and 98152/1993).
The above-mentioned polyamide exhibits very excellent impact resistance, heat resistance, mechanical properties, chemical properties and physical properties, but causes a white powder to precipitate in the metal mold when the injection molding is repetitively executed by using a metal mold. When used for the electronic devices, furthermore, the polyamide exhibits insufficient anti-creeping property under high temperature and high humidity conditions, and it has been desired to improve this property.
The present inventors have analyzed the powder and have found the fact that the powder contains residual monomers, oligomer components and decomposed products of polymers. The unreacted monomers, low-order oligomers and decomposed products of polymers bring about problems such as impairing the appearance, deteriorating dimensional precision, etc. when the electronic parts are to be molded and, particularly, when small parts such as connectors are to be molded. Moreover, the white powder that precipitates in the metal mold causes vent holes of the metal mold to be clogged. Therefore, the molding operation must be interrupted to clean the metal mold.
It has therefore been desired to provide a semiaromatic polyamide resin composition which exhibits excellent mechanical strength such as rigidity, impact resistance, bending strength, and exhibits excellent chemical and physical properties such as anti-creeping property, impact resistance and heat resistance, causes the metal mold to be less fouled during the molding operation, causes no clogging in the vent holes of the metal mold, and makes it possible to obtain precision molded articles exhibiting excellent appearance.